Purpose: :
To assess the relationship between baseline IOP andthe 9–year incidence of OAG in the Barbados Eye Studies(BESs) cohort.

Methods: :
The BESs included 4,709 (84% participation) randomlyselected residents of Barbados, W. I., 40–84 years atbaseline. Surviving cohort members were re–examined at4– and 9–years, respectively. This report is basedon participants of African origin (n= 4,314 at baseline). OAGwas determined by visual field plus optic disc criteria, afterexcluding other possible causes; IOP was not considered. Incidenceof OAG was based on persons who developed OAG in at least oneeye during 9–years, among those without OAG in eithereye at baseline. Cumulative incidences were estimated throughthe product–limit approach. Cox regression models determinedrelative risk (RR) ratios with 95% confidence intervals (CI)for persons at different IOP levels at baseline.

Results: :
The 9–year incidence of OAG (based on 125 incidentcases) increased steadily with higher IOP, from 1.8% with IOP≤17mmHg to 22.3% with IOP>25 mmHg. Among the 431 persons withbaseline IOP>21 mmHg, incidence was 15.6%, vs. 2.8% withIOP<21mmHg, for an overall 9–year population incidenceof 4.4% (95% CI: 3.7%, 5.2%). After adjusting for age, gender,hypertension and IOP–lowering treatment, incidence wassignificantly higher among those with IOP 21–23 mmHg atbaseline, as compared to those with IOP≤17 mmHg (RR=5.4 (95%CI: 2.7, 10.5)). The corresponding RRs were 7.9 and 13.1 forbaseline IOP 23–25 mmHg and >25 mmHg, respectively.While these RRs were high, most persons in the population haveIOP<21mmHg and considerable overlap existed in the baselineIOP of those with and without incident OAG. The attributablerisk (AR) was 37% for IOP >21 mmHg and 19% for IOP >25mmHg.

Conclusions: :
This longitudinal study quantifies the long–termrisk of OAG at different IOP levels, based on a population ofsimilar ancestry to African–Americans. While these newdata confirm the strong relationship between IOP and incidentOAG, they highlight the role of OAG risk factors other thanIOP.